A Relay Node (simply referred below to as an RN) is introduced to a Long Term Evolution-Advanced (LTE-A) system so as to extend network coverage. The RN is connected wirelessly with a Donor evolved NodeB (DeNB). A wireless interface between them is referred to as a Uu interface. The RN does not support a Multimedia Broadcast Multicast Service (MBMS) due to the architecture of the system in the prior art.
A detailed description related to an RN in the prior art will be given below.
In a future mobile communication system, e.g., in a Beyond Third Generation (B3G) system or in an LTE-A system, the system will provide higher peak data rates and a higher cell throughput and also require a higher bandwidth, and since there is few unallocated bandwidth below 2 GHz at present, a part or all of the bandwidth required for the B3G system has to be located in a higher frequency band, for example, the bandwidth required for the B3G system has to be sought in a frequency band above 3 GHz. A propagating electric wave will be attenuated faster and transmitted over a shorter distance in a higher frequency band, so a larger number of eNBs will be needed in the same coverage area so as to ensure continuous coverage, and this will undoubtedly increase the cost of network deployment because the eNBs are generally relatively expensive. In order to address the issues of network deployment cost and coverage, various manufacturers and standardization organizations come to research the introduction of an RN to a cellular system so as to extend the coverage area.
In the network of the LTE-A system with an RN introduced thereto, the RN accesses a core network over a donor cell served by a DeNB and has no direct wired interface with the core network, and each RN can control one or more cells. In this architecture, there is an interface referred to as a Uu interface between a User Equipment (UE) and the RN, and there is an interface referred to as a Un interface between the RN and the DeNB.
In the architecture of the LTE-A system with the RN introduced thereto, the RN has the following dual identity.
Firstly, the RN has the identity of a UE, and the RN is started up similarly to a power-on attachment procedure of a UE. The RN has to be connected to a Serving Gateway (SGW) or a Packet Data Network (PDN) Gateway (PGW), and a control node which is a Mobility Management Entity (MME).
Secondly, the RN has the identity of an eNB for a UE accessing the RN, and in this case, downlink data of the UE has to be transmitted from the SGW or the PGW to a serving eNB of the UE, i.e., the RN, and then transmitted from the RN to the UE via the Uu interface.
In a process of establishing an Evolved Packet System (EPS) unicast bearer in the scenario with a deployed RN, a PGW to which the UE is connected triggers the EPS dedicated bearer of the UE to be established. The EPS unicast bearer specific to the UE will be mapped onto an air interface unicast Radio Bearer (RB) between the RN and the DeNB via the Un interface. The DeNB can map the EPS unicast bearer onto an established Un interface unicast RB (if the DeNB maps the EPS unicast bearer onto an established Un interface unicast RB, then the DeNB will trigger a procedure of updating the RB so as to allocate more transmission resources for the RB) or reestablish a new Un interface unicast RB for the EPS unicast bearer.
In the prior art, each EPS bearer includes a Quality of Service (QoS) parameter attribute, and the DeNB maps EPS bearers with similar QoS requirements onto the same RB via the Un interface for transmission under a mapping rule preconfigured on the DeNB.
An MBMS system architecture and a process of establishing an MBMS bearer will be introduced below.
In the MBMS system architecture, an M1 interface is a pure user plane interface defined between an eNB and a Multimedia Broadcast Multicast Service (MBMS) Gateway (GW), and the M1 interface provides non-guaranteed transmission of user plane data between the MBMS GW and the eNB. An M2 interface is a control plane interface defined between the eNB and a Multi-Cell/Multicast Coordination Entity (MCE), and the M2 interface is generally configured to manage an MBMS session and to supply MBMS scheduling information. An M3 interface is a control plane interface defined between an MME and the MCE, and the M3 interface is generally configured to manage an MBMS session.
As specified in the 3GPP TS 23.246, a Broadcast-Multicast Service Centre (BM-SC) triggers an MBMS session initiation flow in which the MBMS GW, the MME and the eNB are involved. An Evolved Universal Terrestrial Radio Access Network (E-UTRAN) is responsible for reserving a resource at an air interface for transmission of MBMS bearer data. The eNB obtains MBMS user plane data from the MBMS GW by joining an IP multicast group.
In summary, a normal eNB in the prior art can control all or a part of cells served by the eNB according to scheduling information of the MCE to participate in transmission of an MBMS. Given a scenario with hybrid deployment of an RN and the normal eNB, however, the RN does not support transmission of the MBMS on one hand, and a general deployment scenario of the RN relates to extension of coverage (a UE can only receive signals from the RN in the extended coverage) on the other hand, so a UE may fail to receive the MBMS normally once the UE moves to a coverage area of the RN, thus seriously influencing the experience of a user.